Added test for previous crash on failed import fix

Also, rewrote the fix a bit.
ref #383.

_pytest/assertion/rewrite.py

@@ -56,13 +56,12 @@ class AssertionRewritingHook(object):
         names = name.rsplit(".", 1)
         lastname = names[-1]
         pth = None
-        if path is not None and len(path) == 1:
-            try:
+        if path is not None:
+            # Starting with Python 3.3, path is a _NamespacePath(), which
+            # causes problems if not converted to list.
+            path = list(path)
+            if len(path) == 1:
                 pth = path[0]
-            except TypeError:
-                # Starting with Python 3.3, `path` started being unsubscriptable, we have to wrap it
-                # in a list.
-                pth = list(path)[0]
         if pth is None:
             try:
                 fd, fn, desc = imp.find_module(lastname, path)

testing/acceptance_test.py

@@ -307,6 +307,24 @@ class TestGeneralUsage:
                 '*ERROR*',
             ])
             assert result.ret == 4  # usage error only if item not found
+    
+    def test_namespace_import_doesnt_confuse_import_hook(self, testdir):
+        # Ref #383. Python 3.3's namespace package messed with our import hooks
+        # Importing a module that didn't exist, even if the ImportError was
+        # gracefully handled, would make our test crash.
+        testdir.mkdir('not_a_package')
+        p = testdir.makepyfile("""
+            try:
+                from not_a_package import doesnt_exist
+            except ImportError:
+                # We handle the import error gracefully here
+                pass
+            
+            def test_whatever():
+                pass
+        """)
+        res = testdir.runpytest(p.basename)
+        assert res.ret == 0
 
 
 class TestInvocationVariants: